The present invention relates to a superconducting magnet abnormality detection apparatus used in ultrahigh speed electromagnetic levitation type trains or the like running at high speed by using electromagnetic levitative force.
As electromagnetic levitation type trains using superconducting magnets, various schemes have been devised. In a practical scheme, levitation ground coils for levitating train bodies and propulsion ground coils for propelling the train bodies are laid down on the track plane of the ground side whereas superconducting magnets are mounted on trains.
FIGS. 2 and 3 are schematic sectional views showing arrangement of coils on superconducting electromagnetic levitation type trains of the prior art. In each of the drawings, a vehicle 80 and a truck 5 mounted under the vehicle 80 are placed in a U-shaped track 81, which surrounds the vehicle 80 and truck 5 at the bottom and on both lateral sides. On both sides of the truck 5, superconducting magnets 1 are arranged at fixed pitches so that S poles and N poles may appear alternately in the running direction of the vehicle 80. Typically, superconducting coils 2 of the superconducting magnets 1 are cooled to extremely low temperature and kept at low temperature. Therefore, each superconducting coil 2 is installed in a vacuum container 3 (hereafter referred to as outer vessel) made of a non-magnetic material, and held so that heat may not penetrate therein from the outside. As shown in FIGS. 2 and 3, superconducting coils 2 housed in the outer vessels 3 of the superconducting magnets 1 and held by load supports 4 are so disposed as to be opposite to both side faces of the track 81. Paying our attention to ground coils for levitating the vehicle 80, it is understood that the ground coils 92 are placed on the horizontal plane of the track 81 in FIG. 3, whereas in FIG. 2 the superconducting coils 2 and the levitation ground coils 90 are respectively disposed on side faces of the truck 5 and the track 81 so as to be opposite to each other. Each of these ground coils 90 shown in FIG. 2 takes such a shape that an upper rectangular coil and a lower rectangular coil are coupled and short-circuited to form a character "8". On the other hand, propulsion ground coils 91 are attached to side walls of the track 81 as shown in FIGS. 2 and 3, and excited by a three-phase AC power source, which is not illustrated, to generate propulsive force in the superconducting coils 2. The superconducting coils 2 generate DC magnetic fields each having a high magnetic flux density and linkage with the levitation ground coils 90 or 92. As the vehicle 80 runs, the DC magnetic fields move. Therefore, the flux linkage with respect to the ground coils 90 or 92 changes. In each of the levitation ground coils 90 or 92 formed by short-circuit coils, a short-circuit current is induced so as to cancel the change in the flux linkage. Induction levitative force is generated between levitation ground coils 90 or 92 and the superconducting coils 2. The vehicle 80 is thus levitated without contact.
When the train is running at 500 kilometers per hour, a higher harmonic pulsating component exists in a magnetic field distribution generated by a current induced in each of the levitation coils 90 or 92. During running, therefore, a pulsating magnetic flux is always incident upon each of the superconducting magnets 1. Typically, each of the outer vessels 3 is made of a conductive material such as A1. By the incident higher harmonic pulsating magnetic flux, therefore, an eddy current flows in each of the outer vessels 3. Between the intense DC magnetic field generated by each of the superconducting coils 2 and this eddy current, electromagnetic force is generated. While the train is running, the electromagnetic force continues to vibrate the superconducting magnet 1. As for the track 81, the track face is made smooth as far as possible. However, the track face is not completely smooth. Furthermore, the coils 90, 91 and 92 attached to the track 81 also have unevenness caused by mounting errors. Therefore, the superconducting magnets 1 are subjected to vertical, lateral and rotational force and vibrate. Especially, the load supports 4 supporting the superconducting coils 2 are always subjected to these vibrations during running.
If any one of the load supports 4 breaks down, the associated superconducting coil 2 loses its support and large vibration is caused. In some cases, the levitative force and the propulsive force cannot be propagated to the truck 5, resulting in a fear of being unable to run. Therefore, it has been considered to measure vibration and strain by attaching acceleration sensors or strain gauges to superconducting magnets 1 and monitor the vibration and strain during running.
Furthermore, it is possible that the superconducting magnets 1 transfer from the superconducting state to the normal conducting state under the influence of the above described vibration and pulsating magnetic flux. If one of superconducting magnets disposed on one side of the truck 5 transfers to the normal conducting state, the number of normal superconducting magnets 1 mounted on one side of the truck 5 differs from the number of normal superconducting magnets 1 mounted on the other side of the truck 5. Therefore, the levitative force and propulsive force exercised upon the truck 5 on one side differs from those on the other side. If the truck 5 continues to run in an unbalance state, abnormal force is applied to the truck 5. In the worst case, there is a fear of contact of a magnet 1 with the side wall of the track 81. Therefore, it has been considered to attach instrumentation lines for voltage detection to the superconducting coils 2 and detect voltage generated when a magnet 1 has transferred to the normal conducting state.
In order to early detect crack or failure caused in the load supports 4, a large number of acceleration sensors or strain gauges are attached to the superconducting magnets 1 in the prior art. The acceleration sensors and strain gauges measure acceleration and strain caused at points where they are attached. For monitoring the vibration of the entire superconducting coil 2, therefore, it is necessary to dispose a large number of sensors beforehand in locations where abnormality is supposed to tend to occur.
In case a large number of sensors are mounted, however, reliability of the sensors must be sufficiently high. Furthermore, for accurately measuring the vibration of the superconducting coils 2 and voltage generated at the time of transfer to the normal conducting state, sensors must be directly attached to the coils 2. Heat is conducted from the outside via the instrumentation line or power supply line. The amount of consumption of liquid helium for cooling the superconducting coils 2 has thus increased.
Furthermore, in case a superconducting coil 2 has transferred from the superconducting state to the normal conducting state, there is a possibility of occurrence of high voltage on an instrumentation line for voltage detection. Therefore, there is a fear of eventual dielectric breakdown of the instrumentation line or fault of a monitoring device.